Type Ibn supernovae from ultra-stripped supernova progenitors

TL;DR

This study investigates whether ultra-stripped SNe can appear as Type Ibn SNe when a dense CSM forms shortly before core collapse. Using a motivated progenitor that ejects $\sim 0.2\,M_\odot$ of CSM 78 days prior and produces $0.06\,M_\odot$ of ejecta with $E_{\rm expl}=9\times10^{49}$ erg, the authors couple 2D explosion results to a 1D STELLA light-curve calculation with modified error control and smearing to capture interaction effects. The findings show that CSM interaction can dominate the early luminosity, yielding a peak around $3\times10^{43}$ erg s$^{-1}$ and radiated energy of $\sim 3\times10^{49}$ erg within 30 days, with the rise time governed by diffusion through the CSM. This work suggests a plausible channel linking ultra-stripped SNe to Type Ibn SNe and motivates broader exploration of pre-SN mass loss in compact binaries to assess the diversity of Ibn-like transients.

Abstract

Ultra-stripped supernovae are core-collapse supernovae from progenitors that lose a significant fraction of mass because of the binary interactions with their compact companion stars. Ultra-stripped supernovae have been connected to fast-evolving faint Type Ib or Ic supernovae. Here, we show that in some cases ultra-stripped supernovae can result in Type Ibn supernovae. Progenitors of ultra-stripped supernovae may trigger violent silicon burning shortly before the core collapse, leading to mass ejection that results in a dense circumstellar matter. By taking an ultra-stripped supernova progenitor that loses 0.2 Msun at 78 days before the core collapse, we compute the light-curve evolution of the ultra-stripped supernova within the dense circumstellar matter. The core collapse results in a supernova explosion with an ejecta mass of 0.06 Msun and an explosion energy of 9e49 erg. Because the dense circumstellar matter is more massive than the supernova ejecta, the ejecta are immediately decelerated and the light curve is powered mainly by the circumstellar interaction. Therefore, this ultra-stripped supernova is likely observed as a Type Ibn supernova. We suggest that some Type Ibn supernovae may originate from ultra-stripped supernova progenitors losing significant mass shortly before their explosion due to violent silicon burning.

Figures (7)

• Figure 1: Density (top) and velocity (bottom) structure of the ultra-stripped SN model shortly before the shock breakout (2,072 sec after core collapse) as obtained by muller2018. This structure is the initial condition for the light-curve model without CSM. Alt text: Line graph. The x axis is the radius ranging from 1 to 6 in the unit of one trillion cm in both top and bottom panels. The y axis of the top panel is the density in g/cc in log ranging from -18 to -4. The y axis of the bottom panel is the velocity in 1000 km/s ranging from -2 to 20.
• Figure 2: Density (top) and velocity (bottom) structure of the CSM at 0.17 days after shock breakout. The SN ejecta at 0.17 days after shock breakout are also presented. The synthetic light curves with CSM are computed by setting this structure with the SN ejecta and CSM as the initial condition. Alt text: Line graph. The x axis is the radius in cm in log ranging from 13 to 16 in both top and bottom panels. The y axis of the top panel is the density in g/cc in log ranging from -18 to -7. The y axis of the bottom panel is the velocity in 1000 km/s in a log scale ranging from 0.01 to 100.
• Figure 3: Top: Synthetic light curves of ultra-stripped SNe with and without CSM. The bolometric light curves are presented by the solid lines. The integrated luminosity in the optical wavelength range ($3250-8900$ Å) is presented by the dashed lines. The synthetic light-curve model from the same explosion model computed by maunder2024 is presented for comparison. Note that the light-curve model of maunder2024 does not take the initial cooling phase into account. Bottom: The same as the top panel but with a longer time range. Alt text: Line graph. The x axis is the time after explosion from 0 to 30 days in the top panel and from 0 to 400 days in the bottom panel. The y axis is the luminosity in erg/s in log ranging from 40 to 45 in the top panel and from 37 to 45 in the bottom panel.
• Figure 4: Photospheric velocity evolution of ultra-stripped SNe with and without CSM. The photosphere is defined at the location where the Rosseland-mean optical depth become $2/3$. The photospheric velocities are plotted only during the phases when the SN is optically thick. Alt text: Line graph. The x axis is the time after explosion from 0 to 30 days. The y axis is the photospheric velocity in 1000 km/s in a log scale ranging from 0.1 to 100.
• Figure 5: Synthetic light curves of ultra-stripped SNe with and without CSM in the optical ($ugriz$) bands. Alt text: Line graph. The x axis is the time after explosion from 0 to 30 days. The y axis is the absolute magnitude ranging from -14 to -19.